1. Field of the Invention
The present invention relates to electric power systems, and more particularly to a method and apparatus for hot swap of modules for electric power systems.
2. Description of the Related Art
Electric systems used in complex environments such as aerospace systems, more electric aircraft systems, industrial environments, vehicles, etc., include a large number of electric modules. Various electric modules may need to be extracted and replaced with other electric modules, to change functionality or to replace electric modules that exhibit faults.
Hot swap, hot-plug, and hot-dock are terms used interchangeably to refer to the process of safely inserting or removing cards, PC boards, cables, and/or modules from a host system without removing power. The goal of hot swap is to insert or remove modules without disturbing, damaging, or degrading up/down-stream adjacent line replaceable modules/subsystems, to increase system availability, reduce down time, simplify system repair, and allow for system maintenance/upgrade without interrupting service to other loads.
If not designed for properly, hot swap can cause severe electrical, mechanical, thermal and operational problems in an electrical system. For example, random pin arcing may occur during the mating process of a replaceable module with its parent electrical system. Pulling a board/module out while there is current passing through the module connectors, or inserting a board/module with all bulk/bypass capacitors at zero volts, can introduce severe electrical voltage/current transients which may adversely impact reliability and lead to safety consequences. For example, current chopping introduces Ldi/dt variations (where L is inductance of a load, for example) leading to very large voltage transients which are a major safety concern for maintenance people, as large voltage transients can cause high voltage electrical shock.
Typical/conventional hot swap methods do not cover hot swap technologies for higher AC and DC power systems for safe and reliable insertion and removal of different types of line replaceable modules (LRMs) such as: Power Supplies (PS-LRM), Digital Controllers (DC-LRM), AC Solid-State-Remote-Controllers (AC-SSPC-LRM), DC Solid-State-Remote-Power-Controllers (DC-SSPC-LRM), boards including AC and DC Solid State Switching Devices (SSSDs). Such AC and DC power systems may have AC voltages of 115 or 230V, or higher, with fixed frequencies (for example, 50/60 Hz or 400 Hz), or variable frequencies (for example 360-800 Hz for aerospace applications), or DC voltages levels such as, for example, 28V or 270V. The power of such AC or DC systems may depend on the number of channels and current rating and voltage of each channel. For example, an AC LRM for the Airbus A380 aircraft has 8 channels. Such AC and DC LRM boards are currently being deployed in aerospace and industry, and are poised to eventually replace traditional electromechanical AC/DC circuit breakers or relays, to reduce the overall system cost and weight, and improve reliability. Emerging Solid State AC and DC switches are poised to have widespread use in both commercial and military aerospace applications and general industry, for a few Watts to hundreds of KW power applications. Currently, due to excessive cost, weight and board space penalties, AC and DC SSPC LRM cards do not include additional circuit breakers or relays which could be turned-off before initiating a hot swap of a failed LRM with one or more SSPC devices failed short. Hence, conventional hot swap is not properly designed for such LRM/boards. Conventional methods focus on hot swap of boards with fairly low power supply voltages. Even though hot swap technologies have become an integral part of major operating systems in telecommunications, networking and other computer industries, such hot swap systems have not been utilized for high-voltage AC and DC electrical power systems in the aerospace industry or in industrial environments.
A number of publications have studied hot swap techniques for electrical modules. One such technique is described in “Introduction to Hot Swap”, by Jonathan M. Bearfield, Texas Instruments, TechOnLine, publication date Sep. 24, 2001. In the technique described in this publication, a hot swap system for hot swap of modules includes a connector with long and short pins, a fuse, and an RC circuit. During hot swap of a module, the long pins mate first, adding the RC circuit to pre-charge the module/board. When the board/module is fully inserted, the short pins mate, bypassing the resistor connected to the longer pins and creating a low impedance connection. This technique, however, does not detect board/module insertion or extraction at the beginning of the hot swap process in order to prevent disturbances to various data lines. This technique also does not communicate with the remaining software of the larger electrical system to prevent further abnormal operation or possible damage on circuits surrounding the modules/boards that are hot-swapped.
Another technique is described in patent U.S. Pat. No. 6,006,298 titled “On-Line Module Replacement System”, by Tatsuo Satoh. In the technique described in this publication, two power supplies are connected to two pins and to a plug-in module. One pin (first power supply pin) has an insulated portion that is connected to the plug-in module after the other pin (second power supply pin) has been electrically connected to the plug-in module, so that the first pin is electrically disconnected from the module after the second pin has been electrically connected to the module. In this technique, however, two power supplies and a complex long/short pin system with partially insulated sleeves are needed, and the method is not cost effective. Moreover, this method may cause short on the power supplies, particularly if the voltage levels of the power supplies are different. This method may introduce significant electrical (current/voltage) transients during hot swap due to potential current chopping when pulling a module out of a backplane.
A disclosed embodiment of the application addresses these and other issues by utilizing a method and apparatus for hot swap of modules for AC and DC electric power systems that use either low or high supply voltages. The method and apparatus prevent random pin arcing during mating process by reducing the AC or DC current during the MAKE or BREAK process; eliminate in-rush currents during initial insertion of a board/module with all bulk/bypass capacitors at zero volts; prevent current chopping when a board is pulled-out when there is a load current in a normal or fault situation; eliminate large electrical voltage/current transients, such as large voltage transients due to Ldi/dt current chopping variations, which may adversely impact reliability and lead to safety consequences; detects the process of a board/LRM insertion or extraction. The method and apparatus for hot swap of modules for AC and DC electric power systems can be used for both low and high power systems.